Injection-molding processes are widely used, in particular in the mass production of injection-molded parts of all kinds. Depending on the injection-molded part to be produced, a wide variety of functions, sizes and forms can be encountered.
The injection molding generally takes place in a cyclical sequence that can be repeated as often as desired, one or more injection-molded parts, referred to hereafter as blanks, being produced in each cycle. Liquefied molding material is introduced under pressure into a closed cavity, formed by a generally at least two-part hollow mold and possibly one or more cores, until the cavity is filled, followed by a solidifying process. After that, the cavity is opened, the blank, which in the meantime has hardened to a stable form, is removed, and the hollow mold is closed again.
In the case of particularly small blanks, to increase the efficiency and the number of pieces produced it is expedient to form the injection-molding tool in such a way that it makes it possible to produce a number of blanks simultaneously in one cycle. The molding material can be introduced through a runner leading from outside the injection-molding tool into the cavities thereof. A downstream gating system is responsible for distributing the molding material to the individual hollow molds for the blanks. A so-called molding is thereby produced.
The sprue is formed in the runner, the support system is formed in the gating system and the blanks are formed in corresponding cavities connected to the gating system.
The overall cavity of such an injection-molding tool consequently comprises the runner for forming the sprue, blank cavities for forming the blanks and a cavity which connects these blank cavities to the runner and forms the support system. This connecting cavity generally comprises individual channels. In cases such as the present case, in which many blank cavities are arranged close to one another, it is more expedient however to combine individual channels or even to form a common distributing space.
In such cases, the support system of the molding that is formed in the runner goes over from a branched structure into a two-dimensional structure.
In most cases, the entire molding is demolded completely and as a whole, in that it is discharged from the cavity manually or by a device, in order subsequently to be further processed in a separate working step. The blanks are thereby separated from the support system, usually locations of particularly low material thickness, known as predetermined breaking points, being provided at the transition from a blank to the support system, so that the blank is separated in a controlled manner from its support system at the desired location with little effort, often by simple tearing, shearing or bending.
The removal of the molding from the cavities is a recurrent problem, especially in the case of automated installations. This removal becomes all the more complicated the smaller, more complex and fine-membered the blanks and the support system are, and the more rubber-like or elastic or soft the injected molding material is. If the molding cannot be successfully demolded as a whole, individual regions are left behind or remain stuck in the cavity of the injection-molding tool. Problems also occur during the injection molding as a result of trapped residual air, which can disturb the formation of the surface of the blanks.
Moreover, separating the individual blanks from the common support system is also laborious and complicated to accomplish. A separate operation is generally provided for this after the injection-molding operation. Small blanks, in particular rubber-elastic blanks, also make this operation more difficult.